1. Field of Endeavor
The example embodiments relate to methods of forming isolation structures useful in semiconductor processing, methods of forming semiconductor devices incorporating such isolation structures and semiconductor devices that incorporate one or more such isolation structures. The example embodiments include, for example, methods of forming isolation structures useful in non-volatile semiconductor memory devices, methods of manufacturing non-volatile memory devices incorporating such structures and non-volatile memory devices incorporating such structures.
2. Description of the Related Art
Efforts to increase levels of integration in electronic devices including, for example, integrated circuits and display devices incorporating such integrated circuits, and reduce the overall size of the electronic devices have resulted in design rules that reflect gradually decreasing critical dimensions including, for example, the spacing of adjacent active regions within the devices and/or variations in conductor width and spacing of electrode patterns formed during fabrication of such devices. The design rules also tend to produce openings or recesses having increasing aspect ratios, the result of the recess depth divided by the recess width. Recessed regions having an aspect ratio greater than about nine may be considered to have a relatively high aspect ratio.
A variety of insulating materials have been used in the formation of conventional shallow trench isolation (“STI”) structures including, for example, high density plasma (“HDP”) oxide, undoped silicate glass (“USG”), tetraethyl orthosilicate (“TEOS”) and other materials and combinations thereof well known to those skilled in the art. As is also well known to those skilled in the art, using these conventional materials to fill high aspect ratio recesses presents certain processing and/or potential yield and/or reliability concerns.
In particular, the use of conventional insulating materials to fill the recessed trench regions tends to result in greater deposition rates at or near the surface in which the recess is formed. This increased deposition near the surface opening of the trench regions tends to close the recess prematurely, thereby tending to leave one or more central voids in the material filling the trench. One means for reducing the formation of voids in the isolation structures involves the application of a spin-on-glass (“SOG”) composition that does not exhibit the enhanced deposition rate near the opening of the recess, thereby tending to improve the uniformity of the fill material(s) within the recess.
SOG materials, however, may be contaminated with carbon and/or other conductive materials that have been associated with increased leakage currents, for example, leakage at the interface between active regions and the trench sidewall, that may compromise the performance of the resulting devices. One solution that has been proposed includes the use of both an HDP oxide deposition that partially fills the trench and an upper SOG layer that fills the remainder of the trench, thereby reducing the contact between the SOG and the active regions and reducing the likelihood of void formation within the fill material. Another proposed solution involves the use of a composite oxide-nitride-oxide (“ONO”) insulating layer formed over the SOG. Unfortunately, it has proven difficult to achieve acceptable uniformity in the ONO layer when formed on the SOG layer which may result from variations in the underlying SOG layer, for example, variations in the carbon/organic content of the SOG layer and/or variations in the porosity of the SOG layer, both wafer-to-wafer and/or across a single wafer. Another proposal utilizes a second layer of HDP oxide on the SOG layer rather than an ONO composite layer in order to improve the layer uniformity.
As will be appreciated by one skilled in the art, in the course of depositing and/or forming the various layers of insulating material used to fill the trench isolation opening, similar layers of material are being deposited on the surface of the adjacent active regions. In order to expose the surface of the active regions for subsequent processing, these insulating layers must be removed. Conventional methods of removing this insulating material typically utilize an etch-back (“E/B”) process (sometimes referred to as a blanket etch) and/or a chemical-mechanical polishing (“CMP”) process. The relatively smaller widths of the trench openings found in the cell region or core region when compared with the widths of the corresponding trench openings found in the peripheral region, however, tend to result in excess material being removed from the peripheral region in order to ensure that the removal is substantially complete in the cell regions.
The structures produced by several such conventional methods are illustrated in FIGS. 1-3. As shown in FIG. 1, the first conventional structure includes a lower HDP oxide 31 and an upper SOG material 32 in which an ONO layer is formed in direct contact with the SOG oxide. As noted above, this structure is associated with certain characteristic deficiencies, particularly with regard to reduced uniformity of the ONO layer associated with variations in the properties and/or characteristics of the underlying SOG material. It is also noted that, as illustrated in FIG. 1, the lower HDP oxide 31 forms a trough or bowl-shaped structure in which the SOG material 32 is contained so that the periphery of the lower HDP oxide extends above the surface of the SOG material and, indeed, above a plane defined by the surfaces of the adjacent active regions.
As illustrated in FIG. 2, a second conventional structure includes both a lower HDP oxide 61a that defines a trough or channel-shaped structure in which a SOG material 63a is deposited, with the SOG material being capped with a second HDP oxide 65a. The HDP oxides 61a, 65a may be formed, for example, using a hydrogen injected HDP CVD method. Again, as illustrated in FIG. 2, the lower HDP oxide structure 61a includes peripheral regions that extend above the upper surface of the SOG material 63a, but, unlike the structure illustrated in FIG. 1, includes an upper HDP oxide 65a to cap the SOG material and prevent subsequent layers from being formed on the SOG material surface. The upper HDP oxide 65a also extends above a plane defined by the surfaces of the adjacent active regions, resulting in a surface that is non-planar.
As illustrated in FIG. 3, a third conventional structure includes a lower HDP oxide 12a that defines a trough or channel-shaped structure in which a SOG material 13 is deposited and an upper HDP oxide 12b that caps the SOG material. In this conventional structure, the SOG material typically comprises a hydrogen silsesquioxane (“HSQ”) or a polysiloxane. Again, as in FIGS. 1 and 2, the lower HDP oxide structure 12a illustrated in FIG. 3 includes peripheral regions that extend above the upper surface of the SOG material 13, but, unlike the structure illustrated in FIG. 1, includes an upper HDP oxide 12b to cap the SOG material and prevent subsequent layers from being formed on the SOG material surface and, unlike the structure illustrated in FIG. 2, the surface of the upper HDP oxide is generally co-planar with the surfaces of the adjacent active regions, thereby providing a substantially planar surface for subsequent processing.